Messages in this thread Patch in this message | | | From | Masayoshi Mizuma <> | Subject | [PATCH 1/1] arm64/sve: Fix wrong free for task->thread.sve_state | Date | Thu, 26 Sep 2019 15:08:46 -0400 |
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From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
The system which has SVE feature crashed because of the memory pointed by task->thread.sve_state was destroyed by someone.
That is because sve_state is freed while the forking the child process. The child process has the pointer of sve_state which is same as the parent's because the child's task_struct is copied from the parent's one. If the copy_process() fails as an error on somewhere, for example, copy_creds(), then the sve_state is freed even if the parent is alive. The flow is as follows.
copy_process p = dup_task_struct => arch_dup_task_struct *dst = *src; // copy the entire region. : retval = copy_creds if (retval < 0) goto bad_fork_free; : bad_fork_free: ... delayed_free_task(p); => free_task => arch_release_task_struct => fpsimd_release_task => __sve_free => kfree(task->thread.sve_state); // free the parent's sve_state
Add a flag in task->thread which shows the fork is in progress. If the fork is in progress, that means the child has the pointer to the parent's sve_state, doesn't free the sve_state.
Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> Reported-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> --- arch/arm64/include/asm/processor.h | 1 + arch/arm64/kernel/fpsimd.c | 6 ++++-- arch/arm64/kernel/process.c | 2 ++ 3 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index 5623685c7d13..3ca3e350145a 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -143,6 +143,7 @@ struct thread_struct { unsigned long fault_address; /* fault info */ unsigned long fault_code; /* ESR_EL1 value */ struct debug_info debug; /* debugging */ + unsigned int fork_in_progress; #ifdef CONFIG_ARM64_PTR_AUTH struct ptrauth_keys keys_user; #endif diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 37d3912cfe06..8641db4cb062 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -202,8 +202,10 @@ static bool have_cpu_fpsimd_context(void) */ static void __sve_free(struct task_struct *task) { - kfree(task->thread.sve_state); - task->thread.sve_state = NULL; + if (!task->thread.fork_in_progress) { + kfree(task->thread.sve_state); + task->thread.sve_state = NULL; + } } static void sve_free(struct task_struct *task) diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index a47462def04b..8ac0ee4e5f76 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -347,6 +347,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) if (current->mm) fpsimd_preserve_current_state(); *dst = *src; + dst->thread.fork_in_progress = 1; return 0; } @@ -365,6 +366,7 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, * and disable discard SVE state for p: */ clear_tsk_thread_flag(p, TIF_SVE); + p->thread.fork_in_progress = 0; p->thread.sve_state = NULL; /* -- 2.18.1
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